Drilling wells



FRANK J. CARMAN, OF SAN FRANCISCO, CALIFORNIA.

DRILLING WELLS.

' R0 Drawing.

To all whom it may concern:

Be it known that I, FRANK J. CARMAN, a citizen of the United States, residing at San Francisco, in the county of San Francisco and State of California, have invented certain new. and useful Improvements in Drilling Wells, of which the following is a specification.

This invention relates to drilling wells: and it comprises a method ofdrilling oil and gas wells wherein such drilling is performed in the presence of a circulation of mud, that is, muddy water, containing clay in a flocculated state; all as more fully hereinafter set forth and as claimed.

In one of the usual methods of drilling oil and gas wells, the work is done by a bit or drill mounted on and actuated by a tubular member of constantly increasing length; this member being simply a succession of lengths of pipe screwed together. The bit being of greater width than the pipe, as excavation goes on an annular channel is formed around the pipe. In order to remove the debris, or drillings, a flow of water is maintained down through the pipe and up through the channel; this flow being technically known as a circulation. As the drill oes down it passes successively through all sorts of formations, clays, sands, shales, etc.; some being loose and pervious and some carrying water and some not. As the circulation water is in general under a high hydrostatic head, it tends to flow upward and away wherever the formations are open and pervious, forcing ahead of it such water as may occur. In order to prevent this, it is the custom to use mud instead of water; mud meaning here muddy water carrying 5 to 10 per cent of suspended clay. The clay enters and plugs the pores and crevices in the hole walls and prevents lateral escape of the circulation water. Its use is also advantageous for other reasons. For one thing, the clay enters and compacts sands and other loose formations, making walls which, under the hydrostatic pressure of the circulation water, stand up very well. The mud prevents cavin and gives considerable solidity to the we s, so that in drilling through loose sands, the hole acquires a fair degree of permanence; enough so that the apparatus can be temporarlly taken out of V the" hole for sharpening the bit, etc., without collapse. The hole 1s of course left full of mud during this removal. Drill ng 15 Application flied March 21, 1922. Serial No. 545,574.

continued until oil-bearing or gas-bearing sands or formations are reached, successive portions of the upper bore being cased off from time to time in ways not here important.

While the stated sealing, plugging and wall compacting actions of the mud circulation are highly desirable during most of the drilling, they are apt to be dangerous when the sands or formations carrying gas or oil are reached, for the reason that the sealing may become permanent; the flow of gas or oil may be wholly shut oif. Under the heavy pressure of the water column of the circulation, the finely divided clay may be forced into the sands in such a Way as to be irremovable by the oil or gas when the water is removed.

It is the object of the present invention to retain the advantages of the mud in this circulation while obviating its disadvantages. To this end, advantage is taken of certain of the properties of clay.

Clay is mineral matterin an indefinitely fine state of subdivision; the fineness being so great that much, or most, of it can form colloid suspensions. Muddy water is such a suspension. Clay is usually, though not necessarily, mostly composed of very fine particles of hydrated silicate of alumina. The word clay, however, has more of a physical than a chemical significance. Every natural clay contains particles of many orders of magnitude; some being coarse enoughto settle out of a water suspension quickly and others being fine enough to stay suspended for long periods. In a good clay the fine stuif predominates. The suspende particles obey the general rules of colloid suspensions, the dispersion being increased by some ions and chemicals and being decreased by others. In the clay working arts an increased state of dispersion, or ca ability of dispersion, is termed a defloccu ation of the clay; and, vice versa, a decrease in the state of dispersion is termed flocculation.

These terms reflect physical characteristics.

On adding flocculating bodies to muddy water, the surface state of the fine particles is changed and they are made capable of coming together in flocky, loose clum s or aggregates which tend to settle. 'Floccu ated clay, though it stirs up into water readily, comes out again or settles after stirring is discontinued. The fineness of the ultimate particles is in no way impaired but their ence of water, defiocculating difierent. In the presthese loose flocks into the original fine grained dispersions. On assin water containing clay in t probably being, so to speak, taken upby the sand grains in a way which is analogous to adsorption. slimy sticky, and ad eres with tenacity, being ifiicult to remove. Any sand filter clogged with deflocculated clay is hard to clean and, similarly, it is hard ,to remove deflocc'ulated clay onceit is de osited. in the pervious matter of the walls 0 the well,

In the presentinvention, 'I use a mud circulation as usual; but in the stages where oil and gas ma be encountered, instead of em loying the c a of the mud in its natural dedbcculated con ition, I add to the circulation water a certain amount'of bodies havin a flocculating action on clay. Complete flocculation is not ordinarily desirable, as this would make the mud settle too uickly' and be inconvenient in drilling, but 1; ere should be enough flocculant used to deprive the settlings of their sticky, slimy character.

" Almost any soluble electrolyte ma be employed forthe present purposes. solution of common salt does very well. Calcium chlorid, potassium chlorid, sodium sulfate, etc., etc., will serve. Free lime, that is milk of lime, and other basic lime com.- ponds also have a flocculating action. The caustic alkalies and their carbonates, on the other hand, have a deflocculat'r ng action and are not here -ap licable. 'For this reason, while neutral 'ts of the falkalies are applicable and lime and its carbonate is also applicable, free lime should not be used in "connection with neutral sodium'or potasgigitllili salts. Either may be used but not In using a suspension. of clay in a more or less flocculated state for the circulation, the walls are uite as, welluplu ged or lined under the hy rostatic he 0? tion water, butv the lugging is not permanent-it can be rea 11y removed. The clay having lost its stickiness, or most of it, can be readily dislodged in various ways, the

passage of oilor as. With the muddy e de occulated state through sand, the fine colloid particles are taken out by and adhere to the sand, cla and The de osit in a sand bed is.

of powdered gypsum to the the circulastrata opened up sufiicieritlz to'permit and of the circu ation removed, the oil or gaspressure is usuall suflicient to force a way through. Floccu ated clay has not the slimy, clin' g character of defiocculated an oil sands in the drillin the plugging with defloccula w clay. I 1

In practicin the present invention, I drill the well in t e usual way, employingthe ordinary mud circulationwhile the well is progressing through the surface formations and until 1t reaches the neighborhood of oil and gas formations. At the time, I simply g g add a certain amount of a' flocculatin to the circulation, thereby flocculating the suspended clay to a corres onding extent. The particular amount used depends u. on the character and amount of clay. Wit 5 per cent of suspended clay in the mud, the amount of common salt desirable may ran e from 0.5 per cent to 5 r cent or so in I e case of some highly p astic clays. Strong solutions are sometimes desirable because of their buoying action. A 5 per cent solution has a specific gravity around 1.1.

Instead of using common salt, other saline solutions may be employed. The solid salts may be added to the circulation direct. I may use milk of lime or very finely. divided suspended calcium carbonate. Either will flocculate cla A solutionof calcium chlorid is eflicient for the present purposes. For some pu oses, I ma dissolve more or less gy sum calcium su fate) in this 'calcium c orid solution. A simple addition mud is useful for my purposes;

What I claim is:-

1. In the drilling of oil and gas wells with l the aid of a mu circulation, the process which comprises adding to such a circulation nliaterial having a flocculating efiect upon 0 ay.

2. In the drilling of oil and gas wells with the aid of a mu circulation, the process which comprises adding to such a circula tion .a solution of common salt.

In testimony whereof, I have hereunto affixed my signature. I FRANK J. CARMAN.

though it'enters and plugs gas ydrostatic e6 can'be removed; which is'o 11 not the case 

